During the 2008 campaign, Mr. Reid repeatedly taunted Senator John McCain of Arizona, the Republican nominee, saying he should show leadership. He told a Las Vegas newspaper, “I can’t stand John McCain.”

In 2005, Mr. Reid said of President George W. Bush: “This guy is a loser.” He later apologized for that remark, but stood by another claim that Mr. Bush had been “a liar” while in office.

Mr. Reid called Senator Bill Frist, the Republican leader from 2003 to 2007, “amateurish,” and said in 2007 that Gen. Peter Pace, then the chairman of the Joint Chiefs of Staff, was “incompetent.” Mr. Reid once said that Alan Greenspan, the former chairman of the Federal Reserve, was “one of the biggest political hacks we have in Washington.”…

“It’s a boxer’s instinct,” Adam Jentleson, a spokesman for Mr. Reid, said on Friday afternoon. “You find your opponent’s weak spot, and until he finds a defense, you keep pounding it.”